This invention relates to electro-mechanical actuators, and more particularly to electro-mechanical actuators which release their loads in the event of actuator failure.
Shube U.S. Pat. No. 4,858,491 (which is hereby incorporated by reference herein) shows so-called fail-free electro-mechanical actuators and discusses the operating principles of such actuators. Basically, the actuators shown in the '491 patent have two drive motors that normally operate at the same speed. If either motor ceases to keep up with the other motor, the actuator is automatically decoupled from its load. Most of the embodiments shown in the '491 patent are linear actuators, although the embodiment shown in FIG. 11 is a rotary actuator.
There is increasing interest in the rotary form of fail-free actuators because they offer the potential for being smaller, for having fewer components, and for therefore being cheaper and more reliable than the linear form of fail-free actuators. For example, in the linear actuator shown in FIG. 1 of the '491 patent the threaded shaft and threaded follower required to convert the rotary motion of the drive motors to linear actuator output motion can be eliminated in a rotary actuator. It would therefore be desirable to further optimize fail-free actuator mechanisms for rotary output.
In the embodiments shown in the '491 patent the motors rotate in opposite directions and a reversing mechanisms 52c reverses one of these rotations downstream from monitor differential 16 but upstream from the gear 56 which sums the two motor outputs to drive the actuator output. In the interest of further optimizing the fail-free actuator mechanism it would be desirable to eliminate this reversing mechanism.
In view of the foregoing, it is an object of this invention to improve and simplify fail-free electro-mechanical actuators.
It is a more particular object of this invention to improve and simplify rotary output, fail-free, electro-mechanical actuators.